This invention relates to the removal of solvent. In one of its aspects, this invention relates to the removal of residual solvent from particulate crumb produced by solution polymerization. In another of its aspects, this invention relates to a process for further removal of residual solvent from solution polymerization particles after the particles have been treated by powder form evaporation. In still another aspect of the invention, it relates to an integrated process for removal of solvent using inert gas which is then recycled for further use.
The removal of residual solvent from solid polymer particles such as solution rubber is difficult because there is residual solvent dissolved in the solid polymer which must diffuse from the polymer to be removed. This makes the process of residual solvent removal from these solution polymers time dependent. Although most of the solvent can be removed from the surface of the polymer by various evaporative techniques, solvent will still remain dissolved in the polymer. Gas purging can only remove solvent from the particle surface and this can be done in a short period of time. With the realization that there must be time for the dissolved solvent to diffuse from the polymer particles, it has become apparent that continuous purging of the polymer particles would only be a waste of gas and would complicate recovery of solvent from the purge gas since it would be present in a low concentration. The present invention provides an intermittent procedure for purging the polymer which greatly reduces the volume of inert gas used and inherently enhances solvent recovery since the same amount of purged solvent will be contained in a greatly reduced volume of purge gas.
It is therefore an object of this invention to provide a method for removing residual solvent dissolved in particulate crumb produced by solution polymerization. It is another object of this invention to provide a polymeric product made by solution polymerization from which dissolved, residual solvent has been at least partially removed.
It is still another object of this invention to provide a method for recovering polymer produced by solution polymerization processes from the solvent of the process using a method for substantially removing solvent from the surface of the polymer, particularly powder form evaporation, and then removing residual solvent that has been dissolved in the polymer with an integrated process for collecting inert purge gas with recovery and recycle of the purge gas.
Other aspects, objects and the various advantages of this invention will become apparent on reading the specification and claims of this disclosure in conjunction with a study of the drawing.